Language & WorldFact
Cologne is really just the word 'colony'.
In AD 50, Emperor Claudius raised the settlement on the Rhine to city status: 'Colonia Claudia Ara Agrippinensium', named after his wife Agrippina, who was born there. Only 'Colonia' survived, which Frankish mouths wore down to 'Köln'. French 'Cologne' and 'Eau de Cologne' still show the original.
Useful: Cities with a Latin remnant like Cologne reveal their Roman founding.
Source: en.wikipedia.org